Analog-to-digital converter having reduced circuit area

ABSTRACT

In an analog-to-digital converter, a plurality of divided output currents are produced by dividing at a predetermined ratio each of a plurality of comparison output currents that are produced for each reference potential, and an output voltage generated by each divided comparison output current is further divided by an output means into a plurality of output voltages. A combination of output voltages which are in reversed-phase, and the relationship of which in magnitude is reversed at an intermediate potential between first and second reference potentials, is selected from the plurality of output voltages produced by the above division. According to this construction, comparison outputs of an input analog signal with respect to arbitrary virtual potentials between the two reference potentials actually given can easily be obtained.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a voltage comparison circuit and moreparticularly, to a voltage comparison circuit used for the signalcomparing section of an analog-to-digital converter.

2. Description of the Related Art

Presently, a comparator is used in various signal processing circuits toprocess an analog signal by converting it to a digital signal.

In particular, a large number of comparators are incorporated in ananalog-to-digital conversion circuit (hereinafter called A-D conversioncircuit) which converts an analog signal into a digital signal bycomparing an analog signal with many reference voltages.

However, in the A-D conversion circuit, with the increase of theresolution, comparators need to occupy a very large part of anintegrated circuit, thus unavoidably increasing the area of the entireintegrated circuit. Therefore, a comparator is now required of a typewhich can produce comparison outputs as a result of simultaneouscomparison with a plurality of reference voltages even in a smallcircuit area.

A comparator of the above type is shown in FIGS. 1 and 3, and thecharacteristics of the output voltage is shown in FIGS. 2 and 4respectively. Here, the comparator shown in FIG. 1 is explained. Thecomparator sets the resistances of load resistors connected todifferential amplifiers as different values in accordance withrespective reference voltages V_(REF) and outputs the comparison withrespect to a virtual voltage by comparing the output voltages of twodifferential amplifiers.

In this comparator, the resistances of the load resistors R1 and R2connected to a differential amplifier 1A (including transistors Q1 andQ2) that receives an input voltage V_(IN) and a reference voltageV_(REF1), and the resistances of the load resistors R3 and R4 connectedto a differential amplifier 1B (including transistors Q3 and Q4) thatreceives an input voltage V_(IN) and a reference voltage V_(REF2),(=V_(REF1) +ΔV) are set at a ratio of 3:1. This comparator can produce acomparison output with respect to a virtual potential that internallydivides the two reference voltages V_(REF1) and V_(REF2) at a ratio of1:3.

This comparator uses the relationship in which output voltages V11 andV12 of the differential amplifiers 1A and 1B are proportional to theirgains G1 and G2 (that is, the resistances of the load resistors), and isbased on the principle that the output voltages V11 and V12 become equalat a potential Vc (a potential at the intersection of a solid line and adashed line in FIG. 2) that is given by following equation: ##EQU1##

That is, the potential Vc at which the two output voltages V11 and V12are equal is obtained by internally dividing the output voltages V11 andV12 at a ratio between the gains G1 and G2. In this example, since theresistances of the load resistors R1 and R2 and those of the loadresistors R3 and R4 are set at a ratio of 3:1, the potential Vc, atwhich the two output voltages V11 and V12 are equal, takes a value thatinternally divides the reference voltages V_(REF1) and V_(REF2) at 1:3.That is, a comparison output can be obtained with respect to a virtualpotential that divides the interval between the reference voltages intofour.

For these analog-to-digital converters, various conversion modes havebeen proposed according to fields of utilization, required accuracy, andvelocity. Especially in fields requiring operation at a specially highspeed, parallel (flash) type analog-to-digital converters are widelyused.

In a parallel type analog-to-digital converter, an input signal V_(IN)is input into comparators in parallel, through which a potential atwhich to invert the logical value of a plurality of the comparativeoutput is converted into binary data as a potential of the input signalV_(IN). For example, a parallel type analog-to-digital converter 23 witha resolution of eight bits is shown in FIG. 5.

That is, the parallel type analog-to-digital converter 23 suppliesreference voltages VRT and VRB to one end and the other end of 256reference resistors R_(R1) to R_(R256) connected in series, so as togenerate 255 reference voltages respectively across reference resistorsR_(R1) to R_(R256). The analog input signal V_(IN) is then input intocomparators COMP (CA1 to CA255) to which these reference voltages areapplied in order to draw comparisons with the reference voltages (FIG.6).

Subsequently, the analog-to-digital converter 23 supplies an encoder 25with the comparative output of comparators CA1 to CA256 via adifferentiator 24 composed of AND circuits AND1 to AND255 so that theinput signal V_(IN) should be converted into 8-bit digital data.

However, since parallel type analog-to-digital converters areanalog-to-digital converters designed for high-speed operation, theyneed an extremely large number of comparators. For instance, toconstruct a parallel type analog-to-digital converter with a resolutionof eight bits, it used to be needed to provide approximately tenthousand circuit elements, with the result of an unavoidably larger chiparea.

Moreover, analog-to-digital converters designed for specially high speedoperation often need much operating current because each element isoperated with high speed, with the result of no less than several wattsin power consumption on account of their constituent integrated circuitscontaining numerous circuit elements.

Hence, it is desired to realize a parallel-type analog-to-digitalconverter entailing still lower power consumption and a still smallercircuit area.

Furthermore, in the case where the number of element and the chip areaare reduced, the serial-parallel A-D converter circuit is better thanthe parallel A-D converter circuit.

To simplify explanation, a 4-bit serial-parallel A-D converter circuit31 with two bits of high-order and low-order resolution capability,respectively, will be explained below (FIG. 7).

This 4-bit serial-parallel A-D converter circuit 31 Generates three setsof reference voltages V31, V32, and V33 which divide the referencevoltages into four voltage ranges by means of 16 resistances which areconnected in series between the reference voltages (V_(REFT) andV_(REFB)) and first compares by high-order comparators 32 whether or notinput signal V_(IN) is Greater than three sets of reference voltages,and then generates high-order output data D1A and D2A by supplyingpositive-phase comparative output and reverse phase comparative outputfor each reference voltage to an AND circuit 33.

The serial-parallel A-D converter circuit 31 supplies bias voltage tothe current source of low-order comparators corresponding to thisvoltage range, selects three sets of low-order comparators from amonglow-order comparators C01 to C012, and compares three sets of referencevoltages, which divide each voltage range into four equal parts in theselected three sets of low-order comparators, with input signal V_(IN),respectively.

The serial-parallel A-D converter circuit 31 generates low-order outputdata D3A and D4A by supplying comparative output, which is fetched fromthe common load resistance, to common comparators 34A, 34B, and 34C andby supplying their positive-phase comparative outputs and reverse phasecomparative outputs to an AND circuit 34 through a buffer amplifier.

As understood from FIG. 7, the numbers of high-order and low-ordercomparators are determined by the high-order and low-order resolutioncapability (that is, m bits and n bits) and are needed in a quantity of2^(m) -1 and in a quantity of 2^(n) -1, respectively.

Since the high-order comparators are used to roughly classify the upperand lower reference potentials, the number of high-order comparators canbe smaller than that of low-order comparators in general.

However, this high-order comparator needs a fixed circuit area forwiring. Therefore, a converter circuit in which wiring is easy and thenumber of comparators is a few is desired because it needs only a smallcircuit area.

SUMMARY OF THE INVENTION

In view of the foregoing, a first object of this invention is to providea voltage comparison circuit which can produce output voltages at equaloutput speeds even with the use of a small number of elements.

A second object of this invention is to realize an analog-to-digitalconverting circuit which has smaller chip area as compared with aconventional circuit by using a non-linear shape converting method.

A third object of this invention is to realize an analog-to-digitalconverting circuit which has smaller chip area as compared with aconventional circuit by using both of a non-linear converting method(Vernier) and an interpolation method.

A fourth object of this invention is to provide a flashanalog-to-digital converter using a non-linear shape converting methodand an interpolation method.

A fifth object of this invention is to provide a series-parallelanalog-to-digital converter using a non-linear shape converting methodand an interpolation method.

The nature, principle and utility of the invention will become moreapparent from the following detailed description when read inconjunction with the accompanying drawings in which like parts aredesignated by like reference numerals or characters.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a circuit diagram showing a comparator in the first relatedart;

FIG. 2 is a diagram showing an input-output characteristic of thecomparator of FIG. 1;

FIG. 3 is a circuit diagram of a comparator in the second related art;

FIG. 4 is a diagram showing an input-output characteristic of thecomparator of FIG. 3.

FIG. 5 is a circuit diagram of a parallel A-D converter in the thirdrelated art;

FIG. 6 is a diagram for explaining the operation of the A-D converter ofFIG. 5;

FIG. 7 is a circuit diagram of a series-parallel A-D converter in thefourth related art;

FIG. 8 is a graph for explaining the principle of this invention;

FIG. 9 is a circuit diagram of an A-D converter in the first embodimentaccording to this invention;

FIG. 10 is a graph for explaining the operation of the A-D converter ofFIG. 9;

FIG. 11 is a diagram showing the construction of an interpolationcomparator using for the A-D converter of this invention;

FIGS. 12A and 12B are diagrams for explaining the operation of acomparator;

FIG. 13 is a diagram showing the construction of an A-D converter inninth embodiment according to this invention;

FIG. 14 is a basic circuit diagram of a comparator using for the A-Dconverter of FIG. 13;

FIGS. 15 to 18 are diagrams for explaining the operation of thecomparator of FIG. 14;

FIG. 19 is a circuit diagram of a comparator in the tenth embodimentaccording o this invention;

FIG. 20 is a diagram for explaining the operation of the comparator ofFIG. 19;

FIG. 21 is a circuit diagram of a comparator in thirteenth embodimentaccording to this invention;

FIG. 22 is a circuit diagram of a comparator in sixteenth embodimentaccording to this invention;

FIGS. 23 to 27 are diagrams for explaining the operation of hecomparator of FIG. 22;

FIG. 28 is a circuit diagram of a comparator in the seventeenthembodiment according to this invention;

FIGS. 29 to 31 are diagrams for explaining the operation of thecomparator of FIG. 28;

FIG. 32 is a circuit diagram of a series-parallel A-D converter in thetwenty-third embodiment according to this invention; and

FIG. 33 is a circuit diagram of a series-parallel A-D converter in thetwenty-eighth embodiment according to this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Preferred embodiments of this invention will be described with referenceto the accompanying drawings:

A first embodiment of this invention will be explained using FIG. 8.

At first, the full scale expansion principle by resistance division willbe explained.

The input analog signal V_(IN) is attenuated by a voltage gradientdifferent from the voltage gradient of the reference potential V_(REF).Then the full scale of the input analog signal V_(IN) is expanded to thefull scale of the reference potential V_(REF) by comparing theattenuated analog input signal which has been attenuated and thereference potential V_(REF).

Here the voltage gradient of input analog signal V_(IN) is set to onehalf of the voltage gradient of the reference potential. A case will beexplained in which the full scale of the input analog signal V_(IN) willbe expanded to the double of the full scale of the reference voltageV_(REF) by taking an example of the A-D convertor circuit having an8-bit resolution.

Referring to FIG. 8, the transverse axis designates the number of stepswhereas the longitudinal axis designates the reference potential V_(REF)entered to each comparator and the potential of the attenuated analogsignal V_(INi) (i=1, 2, . . . , 255) entered to each comparator.

Here the maximum potential V_(REFT) and the minimum potential V_(REFB)are respectively offered to the comparators CC1 and CC255 located onboth ends of the group of 255 comparators. On the other hand, to thecomparators CC2 through CC254 located in the middle are offered 253reference voltages V_(REFi) (i=2, 3, . . . , 254) that are arranged onthe straight line connecting the maximum V_(REFT) and the minimumV_(REFB) in an interval of a selected voltage.

On the other hand, the input analog signal V_(IN) is attenuated to onehalf of the voltage gradient (shown in a dotted line in FIG. 8) of thereference potential (shown in a solid line in FIG. 8) by each of 256divided voltage resistor connected in series to be offered to eachcomparator CC1 to CC255.

Consequently, at the first comparator CC1 and the 255th comparatorCC255, the potential difference is generated which is one half of thefull scale of the reference voltage (that is, V_(REFT) -V_(REFB)).

Consequently when the input analog signal V_(IN) is varied from themaximum value V_(REFT) to the middle value of the full scale, theposition of the comparator where the value scale of the potential isinverted between a series of attenuated signal and the reference voltageV_(REFi) is moved from the first comparator CC1 to the 255th comparatorCC255.

In this way, the input analog signal V_(IN) can be converted intodigital data by obtaining the position of a comparator C_(iB) where thepotential magnitude relationship between the potential of the attenuatedanalog signal and the reference potential is inverted.

Since the full scale of the input analog signal V_(IN) can be one halfthe full scale of the reference potential V_(REF), the load loaded onthe drive stage which amplifies the input analog signal V_(IN) can bemade smaller and the S/N ratio can be improved.

Overall construction of the embodiment will be explained.

Referring to FIG. 9, reference numeral 51 designates a non-linear A-Dconvertor circuit, having a resolution of N bits as a whole in which theattenuated signal V_(INi) generated by the array of voltage dividingresistors R and the reference voltage Vri generated by the array ofreference resistors r are compared at the comparator CCi and the resultof comparison is output via the encoder 52 and the output controlcircuit 53.

Here the array of voltage dividing resistors R comprises a seriesconnection of n voltage dividing resistors R_(Ai) (i=1, 2, 3 . . . , n).The array of voltage dividing resistors attenuates the input signalV_(IN) by a predetermined degree with the result that n+1 attenuatedsignal V_(INi) (V_(IN0) through V_(INn)) are supplied to each comparatorCCi (CC0, CC1, CC2 . . . , CCn).

In addition, the array of reference resistors r comprises a seriesconnection of n reference resistors r_(Di) (i=1, 2, 3 . . . , n) whichdivides the reference potentials V_(REFT) and V_(REFB) into n+1reference voltages Vr (Vr_(D1) through Vr_(Dn)) to be supplied to theother input end of the comparator CCi.

To each array of a voltage dividing resistors R and each array ofreference resistors r are connected current sources I11 and I12. Thewhole circuit is so constituted that at the common connecting point avoltage fall occurs that in proportion to the resistance value ofresistors R_(Ai) and r_(Di).

Here the conditions shown in the following equations are required to besatisfied so that the result of comparison by the comparators CCi aremade non-linear and the input dynamic range is made to one half level.

    r.sub.D1 +r.sub.D2 +r.sub.D3 +. . . +r.sub.Dn =2×(R.sub.1B +R.sub.2B +R.sub.3B +. . . +R.sub.nB)                               (2)

    R.sub.A(i+1) =αR.sub.Ai (i=1, 2, . . . , n-1)        (3)

At this time, the resistance ratio α determining each resistance valueof respective voltage dividing resistors Ri can be determined bysubstituting the equation (2) with the equation (3).

When the equation (2) is substituted with the equation (3), thefollowing result is given. ##EQU2##

In this particular embodiment, the resistance value for respectivereference resistors r_(Di) (i=1, 2 . . . , n) is equal. Consequentlywhen the value is set to r_(D1), the equation (4) can be modified in thefollowing way. ##EQU3##

When one end is equal to the resistance value of the voltage dividingresistor R_(A1) and the reference resistor r_(D1) are equal to eachother, the item of the resistance value can be eliminated from bothsides of the equation (5).

Thus the following equation (6) is established. ##EQU4##

In order to determine the value for the resistance ratio α isrepresented in the following equation in the following way by using anunknown number β.

    α=1+β                                           (7)

At this time when the nth power of the resistance ratio α is determinedto the second term by using an expansion of the unknown number β, thefollowing equation (8) is given. ##EQU5##

When the equation (6) is simplified by using the equation (8), thefollowing equation (9) is given. ##EQU6## which comprises an unknownnumber β and a constant n.

When the unknown number β is determined by simplifying the equation (9),the following equations (10) and (11) is given. ##EQU7##

Thus it has been made clear that when the equation (10) substitutes theequation (7), the resistance ratio only has to be determined as shown inthe following equation (11). ##EQU8##

Consequently in the case of A-D convertor circuit 51 having a 3 bitresolution, to allow the voltage dividing resistor R and the referenceresistor r to satisfy the conditions of the equation (1) and theequation (2), only eight resistance values have to be connected to eachother which gradually decreases at a ratio of 7/8 (=1-1/8).

Next, the behavior and effect of the embodiment will be explained.

With respect to the above construction, description will be given to twocases; one in which the resistance ratio α of the voltage dividingresistor R_(Ai) is 1 and other cases.

When the resistance ratio α is 1, n voltage dividing resistors R_(Ai)are inclined at the rate of one half of the input signal V_(INi) withrespect to the reference potentials VRi (a straight line connecting thereference potential V_(REFT) and V_(REFB) in FIG. 10) which generatesthe array of reference resistor r and attenuated at a preselected ratio.

Thus respective attenuated signals V_(INi) entered into respectivecomparators CCi is all included within the scope of one half of the fullscale (namely V_(REFT) -V_(REFB) ) of the reference potential withrespect to the highest attenuated signal V_(IN0) with the result thateach attenuated signals V_(INi) that have been compressed into a linearconfiguration.

Consequently respective attenuated signals V_(INi) in a case where theinput signal V_(IN) transforms in the dynamic range, the positions ofthe comparators CCi that intersect the reference voltages V_(REFi) (theposition being designated with a white circle in FIG. 10) successivelytravel from the left upper corner to the right lower corner on astraight line designating the inclination of the reference voltage inaccordance with a decrease in the input signal V_(IN). When the inputsignal V_(IN) is reduced to one half of the full scale of the referencevoltage, the crossing points travel to the right lower corner.

Thus by setting the resistance ratio α of the voltage dividing resistorsR_(Ai) to a constant value and the resistance values of all thereference resistors r_(Di) to one half of the resistance value, thedynamic range of the input signal V_(IN) entered into the A-D convertorcircuit 51 can be only one half of the reference potential. As aconsequence, the load on the amplification step for amplifying the inputsignal V_(IN) and the S/N ratio is largely improved than before.

On the other hand, when the resistance ratio α of the voltage dividingresistor R assumes a value less than 1, the input signal V_(IN) issuccessively attenuated by n voltage dividing resistors R_(Ai). Thepotential of the attenuating signals V_(INn) which are outputted fromthe dividing resistors R_(An) of n-th steps become a potential lower byone half of the full scale of the reference potential (namely V_(REFT)-V_(REFB)) than the potential of the input signal V_(IN) of the inputsignal in the same manner as a case in which the resistance ratio αassumes a value of 1.

By the way, since the resistance values of the voltage dividingresistors R_(Ai) are set in such a manner that it decreasesisometrically in accordance with an increased number of steps, a curvedepicted by the attenuated signal attenuated signal V_(INi) output fromthe middle point of connection of respective voltage dividing resistorsR_(Ai) form a concave form to the downward direction.

Consequently, the position of the comparator CCi where the attenuatedsignal V_(INi) become larger than the reference voltages V_(REFi)relative to the potential of the input signal V_(IN) for the first timemove toward a larger side compared with a case where the resistanceratio α assumes 1.

The relationship between the size of the input signal V_(IN) at thistime and a position where the generated attenuated signals V_(INi)become larger than the reference voltages V_(REFi) will be representedby using black circles as the position of the comparator CCi. When theblack circle is represented on a straight line where the attenuatedsignals V_(INi) are arranged in case where the resistance ratio αassumes 1, the conversion curve forms a concave curve as shown in FIG.10.

In this case it has been made clear that the position where the level ofthe attenuated signals V_(INi) and the reference potentials V_(REFi)shift when the resistance ratio α assumes a value less than 1 moves fromthe position of a white circles (n/10, 2n/10, . . . , n/2, . . . ) on astraight line when the resistance ratio α assumes 1 to the position ofblack circles (4n/10, n/2, . . . , 8n/10, . . . ) on a curve to providea non-linear input output characteristic.

By decoding the input signal V_(IN) with this characteristic curve, thedigital data output from the output circuit 53 becomes the same outputas a decoded signal formed by compressing the input signal V_(IN) into anon-linear configuration.

Besides the dynamic range of the input signal V_(IN) entered into theA-D convertor circuit 51 at this time can be only one half of thereference voltage. Thus the load of the amplification step thatamplifies the input signal V_(IN) can be reduced, and S/N ratio can beconsiderably improved more than before.

In accordance with the above construction, by setting into an isometricrelationship of the resistance ratio α the resistance values of thevoltage dividing resistor array r supplied to comparators CCi byattenuating the input signal V_(IN), the input signal V_(IN) iscompressed into a non-linear configuration to give the same conversionresult as a case in which A-D conversion is effected.

This can eliminate the D-A convertor circuit and the compression circuitrequired for the conventional A-D convertor circuit from the inside ofthe integration circuit thereby further reducing the circuit area.

Since it is not necessary to send back the output signal to the inputside, the construction is suitable for a high speed process and thetiming control can be facilitated.

Next, the other embodiments of this invention will be explained.

With the second embodiment, it is described a case in which the inputsignal V_(IN) entered into the A-D convertor circuit is equivalentlyexpanded twice. However, the present invention is not limited to this,but the invention can be widely applied to a case where the input signalV_(IN) is expanded by a voluntary magnification rate.

With the third embodiment further, it is described a case in which thewhole value of resistance of the voltage dividing resistor array R thatattenuates the input signal V_(IN) is set to one half of the wholeresistance value of reference resistor array r. However, the presentinvention is not limited to this, but the value can be set to avoluntary ratio.

With the fourth embodiment still further, it is described a case inwhich the resistance values of the voltage dividing resistor R_(Ai) areset so that the values stand in an isometric relation to a variable i.However, the present invention is not limited to this but, the voltagedividing resistors can be set so that these can be given in arelationship of other function such as an exponential function, asecondary function.

With the fifth embodiment still further, it is described a case in whichthe resistance values of the voltage dividing resistors R_(Ai) are madesmall relative to the resistance value of the reference resistors r_(Di)and the input signal V_(IN) is equivalently expanded to perform A-Dconversion. However, the present invention is not limited to this, butthe resistance values of the voltage dividing resistors R_(Ai) can bemade large relative to the resistance values of the reference resistorsr_(Di). The input signal V_(IN) can be equivalently compressed toperform A-D conversion.

With the sixth embodiment still further, it is described a case in whichthe input signal V_(IN) is expanded into a non-linear configuration overa whole range thereof to perform A-D conversion. However, the presentinvention is not limited to this, but the input signal V_(IN) can beexpanded into a non-linear configuration only in a partial range and canbe expanded in a linear configuration in other range to perform A-Dconversion.

With the seventh embodiment still further, it is described a case inwhich the same current is allowed to flow to the rated current sourcesI11 and I12 respectively connected to the voltage dividing resistorarray R and the reference resistor array r. However, the presentinvention is not limited to this, but a voluntary ratio of current canbe allowed to flow.

With the eighth embodiment still further, it is described a case inwhich the present invention is applied to a parallel array type A-Dconvertor circuit. However, the present invention is not limited tothis, but it can be applied to A-D convertor circuit of other type.

As described above, the present invention can realize ananalog-to-digital converting circuit with a even smaller circuit area byentering an input analog signal to a plurality of resistors connected inseries, attenuating the input signal with a non-linear voltage gradientvia this resistor array and comparing a attenuating analog signal thathas been attenuated with a reference voltage to which a preselectedvoltage gradient is given.

Next, the ninth embodiment of this invention will be explained.

Before this invention will be explained, the principle of comparisonoutput interpolation using complementary output will be explained usingFIG. 11.

The comparison output of the analog input signal V_(IN) corresponding toa virtual potential bisectional between two reference potentials isobtained by comparing the in-phase output of the initial differentialpair of one comparator with the reverse phase output of the initialdifferential pair of another neighboring comparator.

Here, it will be explained how to obtain the relative output of theanalog input signal V_(IN) corresponding to a virtual potentialV_(VIRT), as a potential intermediate between two reference potentialsV_(REF1) and V_(REF2) in reference to FIG. 11.

Differential amplifiers AMP1 and AMP2 form respectively the initialdifferential pair of comparators constituting an analog-to-digitalconverter and differentially amplify the reference potentials V_(REF1)and V_(REF2) applied to one input terminal and the analog input signalV_(IN) applied to the other input terminal.

The analog-to-digital converter latches comparative output either highor low by applying the in-phase output S1 and the reverse phase outputIS1 of differential amplifier AMP1 to a latch gate 61, and latchescomparative output either high or low by applying the in-phase output S2and the reverse phase output IS2 of differential amplifier AMP2 to alatch gate 62, as shown in FIG. 12B.

Thereby, the analog-to-digital converter draws a comparison of theanalog input signal V_(IN) with the reference potentials V_(REF1) andV_(REF2).

Moreover, the analog-to-digital converter latches comparative outputeither high or low according to the relation between two signals byapplying the reverse phase output IS1 of differential amplifier AMP1 andthe in-phase output S2 of differential amplifier AMP2 to a latch gate63, and outputs the comparative output to a decoder 64.

The output of the latch gate 63 is inverted at a potential intermediatebetween the reference potential V_(REF1), where the output of the latchgate 61 is inverted and the reference potential V_(REF2), where theoutput of the latch gate 62 is inverted, as will be seen from FIG. 12B.

This means that the comparison output of the analog input signal V_(IN)corresponding to a virtual potential V_(VERT), bisectional between tworeference potentials V_(REF1) and V_(REF2), can be obtained from theoutput of the latch gate 63, as shown in FIG. 12A.

Thereby, the number of initial stage differential pairs of comparatorswhich are applied reference potentials can be thinned out to half thenumber of comparators required by resolution, whereby a considerablereduction in circuit area can be brought about compared with the casewhere the comparators depending on resolution are all integrated.

Next, the overall composition of the ninth embodiment will be explained.

FIG. 13 shows a parallel type analog-to-digital converter 70 with aresolution of N bits, which is so constructed as to convert an analoginput signal V_(IN) into digital data by applying the above-stated twoprinciples.

The analog-to-digital converter 70 inputs an attenuated input signalV_(IN) into respective differential amplifiers AMPi (i=0, 1, 2, . . . ,n) forming the initial stage differential pair of comparators and alsoinputs differential output pairs from respective differential amplifiersAMPi (i=0, 1, 2, . . . , n). The in-phase output and reverse phaseoutput of differential amplifiers AMPi and AMPi+1 (i=0, 1, 2, . . . ,n-1) neighboring to each other into latch gates Li (i=0, 1, 2, . . . ,n) and Li1 (i=0, 1, 2, . . . , n-1).

Therein, the analog-to-digital converter 70 generates referencepotentials V_(REFi) (i=0, 1, 2, . . . , n), lowering with apredetermined voltage gradient respectively across n reference resistorsr_(Ei) (i=0, 1, 2, . . . , n) connected between two reference potentialsV_(REFT) and V_(REFB). This array of reference resistors r is connectedto current source I31 supplying constant current.

The analog-to-digital converter 70 also generates attenuated signalsV_(INi) (i=0, 1, 2, . . . , n) as attenuated versions of the inputsignal V_(IN), with different voltage gradients as against referencepotentials V_(REFi) respectively across an array of n voltage dividingresistors R_(Bi) (i=0, 1, 2, . . . , n) connected between two referencepotentials V_(REFT) and V_(REFB). The resistance of voltage dividingresistors R_(Bi) are set at half as much as the resistance of referenceresistors r_(Ei).

The current value of current source I32 supplying the array of thevoltage dividing resistors R with constant current is then set at thesame current value as current source I31 which is connected with thearray of the reference resistors r, whereby the analog-to-digitalconverter 70 can equivalently double the amplitude of the input signalV_(IN).

Moreover, the analog-to-digital converter 70 supplies differentialamplifiers AMPi with the attenuated signals V_(INi) and the referencepotentials V_(REFi) generated respectively across the array of thevoltage dividing resistors R and the array of the reference resistors r,and apply the differential output of attenuated signals V_(INi)corresponding to the respective reference potentials V_(REFi) to latchgates Li (i=0, 1, 2, . . . , n).

The analog-to-digital converter 70 then obtains from neighboringdifferential amplifiers the reverse phase outputs of differentialamplifiers AMPi whose reference potentials are higher than that of thedivided voltages and the in-phase outputs of the other differentialamplifier AMPi+1 whose reference potentials are lower than that of thedivided voltages one of two neighboring differential amplifiers to latchgates Li1 (i=0, 1, 2, . . . , n-1) arranged between latch gates Li.

Thereby, the analog-to-digital converter 70 is enabled to specify wherein between reference potentials to invert the relation of attenuatedsignals V_(INi) with reference potentials and further to judge whetherthe potentials of the attenuated signals V_(INi) thus specified areabove or below the virtual reference potentials V_(VERTi) (i=0, 1, 2, .. . , n-1), approximately bisectional between the reference potentials.The analog-to-digital converter 70 then behaves apparently as if therewere as many comparators as 2n+1.

The analog-to-digital converter 70 outputs to the output circuit 72 avalue corresponding to the potential where the potential of theattenuated signal V_(INi) becomes greater than the reference potentialV_(REFi) or the virtual potential V_(VERTi) for the first time when thelatch output of each latch gate L is input to the decoder 71, and thenoutputs digital data corresponding to the input signal V_(IN) from theoutput circuit 72.

Next, the behavior and advantages of embodiment will be explained.

The following describes the conversion operation of theanalog-to-digital converter 70 when the potential of the input signalV_(IN) input to the analog-to-digital converter 70 in the compositiondescribed above is a little greater in potential than three fourths ofthe full scale.

This potential is very close to the median of the full scale of theinput signal V_(IN), and a boundary reference potential at which thecomparative relation of differential output is inverted in the centraldifferential amplifier of the n+1 differential amplifiers.

Letting this boundary reference potential be V_(REFm), the logical valueof the latch output at latch gate L(m-1)1 which is given to decoder 71is inverted according to whether or not the attenuated signal V_(INm) ishigher than the virtual potential V_(VIRT) (m-1) set nearly at themidpoint between two neighboring reference potentials V_(REFm) andV_(REF) (m-1).

Accordingly, where the logical value is inverted by the latch output ofthis latch gate L(m-1)1, it is evident that the potential of theattenuated signal V_(INm) is closer to the lower reference potentialV_(REFm) of the two reference potentials.

Where the logical value is not inverted by the latch output of the latchgate L(m-1)1, on the other hand, it is judged that the potential of theattenuated signal V_(INm) is closer to the higher reference potentialV_(REF) (m-1)1 of the two reference potentials.

The analog-to-digital converter 70 can thus convert the input signalV_(IN) into digital data with sharper resolution using a virtualpotential (actually not existent) V_(VIRT) _(i) as reference potentialand hence provides even higher accuracy.

The analog-to-digital converter 70 in the above-described constructioncan equivalently double the amplitude of the input signal V_(IN) byattenuating the input signal V_(IN) through the array of the voltagedividing resistors R, and inputting the attenuated signals V_(INi) thusattenuated to the differential amplifiers AMPi to draw a comparison withthe reference potentials V_(REFi), whereupon the amplitude of the inputsignal V_(IN) may be lowered with the result of an improvement insignal-to-noise ratio.

Moreover, the analog-to-digital converter 70 can substantially reducethe number of elements in relation to resolution by latching throughinputting the reverse phase differential output components of thedifferential output of two neighboring differential amplifiers to thelatch gates.

Next, the tenth embodiment of this invention will be explained.

The concrete circuit construction of the principle of comparison outputinterpolation by dividing complementary output current will beexplained.

In the ninth embodiment, the differential outputs of differentialamplifiers are used as it is, and then the comparison outputs of avirtual potential bisectional between two reference potentials and anattenuated signal are formed by comparing the reverse phase differentialoutput components out of the differential voltage outputs of twoneighboring differential amplifiers with each other. For the tenthembodiment, virtual potentials quadrisectional and more preciselyisotomic between two reference potentials are realized by dividing thedifferential currents of differential amplifiers.

In the case of tenth embodiment, the comparison outputs of a pluralityof virtual potentials intermediate between two reference potentials andattenuated signals V_(INi) are determined by comparing compositecurrents as a total obtained by adding the in-phase output of onedifferential amplifiers AMPi to which attenuated signals V_(INi) andreference potentials V_(REFi) are supplied and the in-phase output ofanother differential amplifiers AMPi+1 to which attenuated signalsV_(INi) and neighboring reference potentials V_(REFi+1) (=V_(REF1) +ΔV)are supplied together in a predetermined proportion with the reversephase output of either amplifiers AMPi or AMPi+1.

The following explains this principle by using two sets of differentialpairs 81 and 82 as shown in FIG. 14. Therein, the differential pair 81consists of transistors Q51 and Q52, to the bases of which an attenuatedsignal V_(INi) and a reference potential V_(REF2) are supplied. Thedifferential pair 82, on the other hand, consists of transistors Q53 andQ54, to the bases of which an attenuated signal V_(INi) and a referencepotential V_(REF1) are supplied.

Letting the collector currents then flowing through transistors Q51,Q52, Q53, and Q54 be IA0, IB0, IC0, and ID0, respectively, the currentvalues of the respective collector currents IA0, IB0, IC0, and ID0 areinverted respectively at reference potentials V_(REF2) and V_(REF1) asshown in FIG. 15.

Accordingly, the comparison output of the attenuated signal V_(INi)corresponding to the reference potential V_(REF2) can be obtained bycomparing by a comparator the output voltages VA and VB, developing atthe connection nodes of load resistors R51 and R52 and transistors Q51and Q52 through which the collector currents IA0 and IB0 flow.

Also, the comparison output of the attenuated signal V_(INi)corresponding to the reference potential V_(REF1) can be obtained bycomparing by a comparator in which the output voltages VC and VD developat the connection nodes of load resistors R53 and R54 and transistorsQ53 and Q54 through which the collector currents IC0 and ID0 flow.

Similarly, the collector currents IA0 and ID0 are inverted at anintermediate potential V_(REF2) +ΔV/2 between the reference potentialsV_(REF2) and V_(REF1) (=V_(REF2) +ΔV), and the collector currents IB0and IC0 are inverted at an intermediate potential V_(REF2) +ΔV/2,between the reference potentials V_(REF2) and V_(REF1). Hence, thecomparison output of the attenuated signal V_(INi) corresponding to thevirtual potential V_(REF2) +ΔV/2 can be obtained by comparing the outputvoltages VA and VD, or the output voltages VB and VC, by a comparator.

Suppose that the comparison output of attenuated signals V_(INi)corresponding to virtual potentials quadrisectional between tworeference potentials V_(REF2) and V_(REF1) (=V_(REF2) +ΔV) are obtainedby using this relationship.

In this case, three collector currents IA0, IB0, and IC0 are used.

In as much as there is a characteristic relation between voltagedifferences and collector currents such that collector currents increaseor decrease linearly within the range where voltage differences aresmaller, the collector currents IA0 and IC0, as the respective in-phaseoutput of the differential pairs 81 and 82 increase or decrease almostin parallel to each other as shown in FIG. 16, and thus the collectorcurrent IB0, as the reverse phase output of the differential pair 81intersects within a basically linear range.

Therefore, if a composite collector current IG0 (=IA0/2+IC0/2) can begenerated by adding the collector currents IA0 and IC0 togetherrespectively in the proportion of 1/2, the composite collector currentIG0 is represented by a straight line at an equal distance from bothcollector currents IA0 and IC0 and running in parallel to both collectorcurrents IA0 and IC0, so that the collector current IB0 and thecomposite collector current IG0 are inverted at the virtual potential V1(=V_(REF2) +ΔV/4), quadrisectional between the reference potentialsV_(REF2) and V_(REF1).

Therefore, the comparative output of a attenuated signal V_(INi)corresponding to the virtual potential V1 (=V_(REF2) +ΔV/4) can beobtained by comparing the output voltage VB, induced by the collectorcurrent IB0, with the output voltage VG induced by the compositecollector current IG0.

In as much as a similar relation holds good for the three collectorcurrents IA0, IB0, and ID0 as well, the comparison output of anattenuated signal V_(INi) corresponding to the virtual potential V3(=V_(REF2) +3.ΔV/4) can be obtained by generating a composite collectorcurrent IJ0 (=IB0/2+ID0/2) obtained by adding the collector currents IB0and ID0 together respectively in the proportion of 1/2 and thencomparing an output voltage VC induced by the collector current IC0,with an output voltage VF induced by the composite collector current IJ0(See FIG. 17).

Again, the comparison output of an attenuated signal V_(INi)corresponding to the virtual potential V3 which is obtained by comparingthe composite collector current IJ0 with the collector current IC0, mayalso be determined by using the composite collector current IG0 used inthe comparison of an attenuated signal V_(INi) corresponding to thevirtual potential V1.

That is, the comparison output of an attenuated signal V_(INi)corresponding to the virtual potential V3 can be obtained by comparingan output voltage induced by the composite collector current IG0 with anoutput voltage induced by the collector current ID0, as shown in FIG.18.

Thus, in this embodiment, the comparison output of attenuated signalsV_(INi) corresponding to the virtual potentials V1, V2, and V3quadrisectional between two reference potentials V_(REF2) and V_(REF1),is interpolated on the principle of comparing a composite collectorcurrent IG0 or IJ0 which is obtained by adding the in-phase output IA0and IC0 (or else IB0 and ID0) together in the proportion of 1/2respectively with the collector currents IB0 and ID0 (or else IA0 andIC0).

The overall composition of embodiment will be hereinafter explained.

For this embodiment, the analog-to-digital converter supplies anattenuated signals V_(INi) attenuated by an array of resistors R todifferential amplifiers AMPi, determining a plurality of voltage valuesby dividing differential currents as results of comparison withreference potentials, and converting these voltage values into digitaldata through latch gate and a decoder. FIG. 19 shows the basiccomposition of the quadrisectional interpolation type comparator of ananalog-to-digital converter based on this principle.

This comparator divides collector currents at a current ratio of 1:2 asthe comparison output of the reference potentials V_(REF1), V_(REF2),and V_(REF3), and then combines and adds them together, whereby thecomparison output of attenuated signals, V_(INi), corresponding tovirtual potentials quadrisectional between reference potentials,V_(REF1), V_(REF2), and V_(REF3) is obtained.

Differential amplifiers AMP2, AMP1, and AMP0 constituting the comparatoreach have a similar composition, wherein attenuated signals, V_(INi),and the reference potentials, V_(REF2), V_(REF1), and V_(REF0) areapplied respectively to transistors Q60, Q70, and Q80 on the one handand transistors Q61, Q71, and Q81 on the other hand, which respectivelyform differential pairs, and thus collector currents according to thesignal levels of attenuated signals, V_(INi), corresponding to therespective reference potentials are led into the respective differentialpairs.

Therein, the collectors of transistors Q60 and Q61, transistors Q70 andQ71, and transistors Q80 and Q81, each of which set forms a differentialpair, are cascade-connected respectively to three common-base dividingtransistor sets, (Q62, Q63, Q63N, Q62N), (Q72, Q73, Q72N, Q73N), and(Q82, Q83, Q83N, Q82N), whose emitter area ratio is set at 1:2, so thatcomparative collector currents should be divided according to theemitter area ratio.

Moreover, each differential pair of the neighboring differential pairsis so constructed as to connect in common the connectors of the dividingtransistor sets (Q62, Q72) and (Q73N, Q83N), whose collector currentsare divided to a third, and as to obtain an output voltage by composingtwo sets of composite collector currents in an reverse phase relationwith each other.

Thereby, letting the divided collector currents of transistors Q63 andQ73 be IA1 and IC1 respectively, a composite collector current IG1(=IA1/2+IC1/2), obtained by combining the divided collector currents IA1and IC1, each in the proportion of 1/2 flows through load resistor R62connected to the common collectors of transistors Q62 and Q72.

Similarly, letting the divided collector currents of transistors Q72Nand Q82N be ID1 and IF1 respectively, a composite collector current IH1(=ID1/2+IF1/2) obtained by combining the divided collector currents ID1and IF1 each in the proportion of 1/2 flows through load resistor R73Nconnected to the common collectors of transistors Q73N and Q83N.

In as much as the dividing transistor sets (Q62, Q63, Q62N), (Q72, Q73,Q72N) and so forth, are connected respectively to the load resistor sets(R62, R63, R62N), (R72, R73, R72N) and so forth, and output voltagecorresponding to the current values of divided collector currentsdivided according to the emitter area ratio of these transistors andeach composite collector current is obtained across each load resistor.

For this embodiment, comparison output corresponding to a virtualpotential quadrisectional between two reference potentials V_(REF2) andV_(REF1), is obtained by comparing the output voltage developing acrossone load resistor with that developing across another load resistor.

That is, the comparison output of attenuated signals V_(INi)corresponding to two reference potentials V_(REF2) and V_(REF1), isobtained by comparing the output voltage across load resistor R63 withthat across load resistor R62N, and the output voltage across loadresistor R73 with that across load resistor R72N.

Also, the comparison output of an attenuated signal V_(INi)corresponding to a virtual potential V2 (=V_(REF2) +ΔV/2) bisectionalbetween two reference potentials V_(REF2) and V_(REF1) can be obtainedby comparing the output voltage across load resistor R62N with thatacross had resistor R73.

Furthermore, the comparison output of an attenuated signal V_(INi)corresponding to a virtual potential V1 (=V_(REF2) +ΔV/4) bisectionalbetween the reference potential V_(REF2), and the intermediate potentialV2 or quadrisectional between the reference potentials V_(REF2) andV_(REF1) can be obtained by comparing the output voltage across loadresistor R62 through which the composite collector current IG1 flowswith the output voltage across load resistor R63 through which thedivided collector current IB1 flows.

Similarly, the comparison output of an attenuated signal V_(INi)corresponding to another virtual potential V3 (=V_(REF2) +3 ΔV/4),bisectional between the reference potential V_(REF1) and theintermediate potential V2 or quadrisectional between the referencepotentials V_(REF2) and V_(REF1), can be obtained by comparing theoutput voltage across load resistor R62 through which the compositecollector current IG1 flows with the output voltage across load resistorR72N through which the divided collector current ID1 flows.

Thus, the comparison output of attenuated signals V_(INi) correspondingto the virtual potentials V1 and V3 quadrisectional between thereference potentials V_(REF2) and V_(REF1), can be obtained by comparingthe composite collector current IG1 in phase with the attenuated signalV_(INi) with the collector currents IB1 and ID1, in an reverse phaserelation to the attenuated signal V_(INi).

On the other hand, the comparison output of attenuated signals V_(INi)corresponding to two virtual potentials V11 and V13 quadrisectionalbetween two reference potentials V_(REF1) and V_(REF0), adjacent to thereference potentials V_(REF2) and V_(REF1), can be obtained by comparingthe composite collector current IH1 in a reverse phase relation to theattenuated signal V_(INi) with the collector currents, IC1 and IE1, in areverse phase relation to the attenuated signal V_(INi) (see FIG. 20).

Next, the behavior and advantages of embodiment will be explained.

The following explains how the analog-to-digital converter in the aboveconstruction performs conversion operations when the potential of theinput signal V_(IN) is a little lower than the maximum potentialV_(REFT).

It is assumed here that the input signal V_(IN) is then enlarged on theprinciple of full-scale enlargement by resistive division, and therelation between attenuated signals V_(INi) input to differentialamplifiers AMPi and reference potentials is inverted at a certainreference potential V_(REF3).

It follows that such an attenuated signal V_(INi) assumes any potentialbetween intermediate between two reference potentials V_(REF3) andV_(REF2).

Also, it is by comparison between output voltages across load resistorsthat can determine which of the virtual potentials V11, V12, and V13quadrisectional between two reference potentials V_(REF3) and V_(REF2),induces an inversion of the relation between attenuated signals V_(INi)input to differential amplifiers and reference potentials.

For instance, if the logical value of comparison output is inverted bythe comparison output of the output voltages across the load resistorR63 through which the divided collector current IA1 flows and acrossload resistor R62N through which the divided collector current IB1flows, then the attenuated signal V_(INi) must be at a potential alittle higher than the reference potential V_(REF3) and lower than thevirtual potential V11 (at the intersection point P12, in FIG. 20).

Also, if the logical value of comparison output is inverted by thecomparison output of the output voltages across the load resistor R73through which the divided collector current IC1 flows and across loadresistor R73N through which the divided collector current IH1 flows,then the attenuated signal V_(INi) must be at a potential higher thanthe virtual potential V11 and lower than the virtual potential V12 (atthe intersection point P13, in FIG. 20).

Similarly, it can be discriminated that the potential of an attenuatedsignal V_(INi) lies between the virtual potential V13 and the virtualpotential V14 (the intersection point P14, in FIG. 20), and also liesbetween the virtual potential V14 and the reference potential V_(REF2)(the intersection point P15, in FIG. 20).

Thus, the analog-to-digital converter can convert the input signalV_(IN) into digital data with fourfold resolution compared with anactually generated reference potential V_(REF).

The analog-to-digital converter in the above construction canequivalently double the amplitude of the input signal V_(IN), becausethe input signal V_(IN) is attenuated through the array of voltagedividing resistors R, and the attenuated signal V_(INi) thus attenuatedis input to the differential amplifiers AMPi to draw comparisons withreference potentials V_(REFi), whereby the amplitude of the input signalV_(IN) can be reduced with the result of an improvement insignal-to-noise ratio.

Furthermore, the analog-to-digital converter can substantially reducethe number of elements in relation to resolution by dividingdifferential currents at a predetermined ratio and comparing one outputvoltage with another induced by composite collector currents obtained byrecomposing the divided currents.

Consequently, the power consumption of any semiconductor integratedcircuit incorporating such an analog-to-digital converter is reducedcompared with that of conventional ICs, and a reduction in chip area aswell can be brought about.

Furthermore, this invention facilitates the realization of flash-typeanalog-to-digital converters with a resolution of ten or more bits,which are suitable for signal processing for high-precision digitaldisplay for use in high-quality TV image receivers.

Next, the eleventh embodiment of this invention will be explained.

With the tenth embodiment, it has been described above the case wherethe voltage gradient of the input signal V_(IN) to be attenuated byvoltage dividing resistors is set at half the voltage gradient ofreference potentials supplied to each comparator. However, thisinvention is not limited to this, but may be widely applied also tocases where the voltage gradient of the input signal V_(IN) to beattenuated through voltage dividing resistors is set at greater or lessthan half the voltage gradient of reference potentials.

Moreover, with the twelfth embodiment, it has been described above thecase where the resistance ratio of voltage dividing resistors andreference resistors is set at 1:2 and a constant current source 131leading in the same constant current I is connected to each array ofvoltage dividing resistors. However, this invention is not limited tothis case alone, but allows the resistance values of voltage dividingresistors and reference resistors to be set at the same value and theratio of constant current flowing in the constant current sourceconnected to each voltage dividing resistors array to be set at 1:2.

Next, the thirteenth embodiment of this invention will be explained.

In the above-described embodiments, it has been described above the casewhere a circuit for interpolating the differential output ofdifferential amplifiers AMPi by current shunting is composed as shown inFIG. 19. However, this invention is not limited to this case alone, but,as shown in FIG. 21, allows both collector currents of transistors Q102and Q103N of the divided collector currents divided by the transistorsets (Q102, Q103) and (Q103N, Q102N), to be composed into the collectorcurrents of low-order differential amplifiers.

Next, the fourteenth embodiment of this invention will be explained.

In the above-stated embodiments, it has been described above the casewhere the differential output of differential amplifiers is interpolatedto determine comparison output corresponding to virtual potentialsbisectional or quadrisectional between reference potentials. However,this invention is not limited to this case alone, but may be widelyapplied also in determining comparison output using virtual potentialseven more precisely isotomic between reference potentials.

Next, fifteenth embodiment of this invention will be explained.

Furthermore, in the above-described embodiments, it has been describedparallel-type analog-to-digital converters. However, this invention isnot limited to them alone, but may be brought similar effects also byusing other analog-to-digital converters, such as the lowest-orderanalog-to-digital conversion processor of a serial-parallelanalog-to-digital converter.

As has been described so far, this invention enables the full range ofanalog input signals to be input to an analog-to-digital converter to beless than the full range of reference potentials, and the comparisonoutput of analog input signals corresponding to virtual referencepotentials isotomic between reference potentials developing across anarray of reference resistors to be obtained, whereby an improvement insignal-to-noise ratio and resolution can be brought about withoutlowering the potential of the least significant digit and also areduction in circuit area can be brought about at no cost of resolution.

Next, the sixteenth embodiment of this invention will be described withreference to the accompanying drawings:

In FIG. 22, reference numeral 110 denotes a whole 6-divisioninterpolation type comparator. In the comparator 110, a collectorcurrent flowing through a differential amplifier 129 is divided into twocurrents at a ratio 1:2, and each of the output voltages resulting fromthe divided collector currents is further halved so that the comparator110 produces four pairs of in-phase and reversed-phase outputs. Thein-phase and reversed-phase outputs of the differential amplifiers 129and 132 are paired and compared with each other so as to producecomparison outputs with respect to virtual potentials that divide theinterval between the reference voltages V_(REF1) and V_(REF2) for therespective differential amplifiers 129 and 132 equally into six.

The differential amplifiers 129 and 132 have the same connection schemein which an input analog signal V_(IN) is compared with the referencevoltage V_(REF1) or V_(REF2) in the first stage differential pair Q121and Q122, or Q126 and Q127. For example, transistors Q123 and Q124 andtransistors Q124N and Q123N, which have different emitter areas, arecascade-connected to the collectors of the transistors Q121 and Q122,respectively, so as to divide the respective differential outputcurrents at a ratio of 1:2.

With the above configuration, collector currents I100 and I101 (=2×I100)that are in-phase with the input analog signal V_(IN) flow throughtransistors Q123 and Q124, respectively, and collector currents I100Nand I101N (=2×I100N) that are in reversed-phase with the input analogsignal V_(IN) flow through the transistors Q124N and Q123N,respectively.

In this embodiment, each of the load resistors connected to thecollectors of the current-division transistors Q123, Q124, Q124N, andQ123N, respectively, consists of two series resistors having the sameresistance (R121, R122), (R123, R124), (R125, R126) or (R127, R128). Thetwo series resistors halve the voltage across the load resistor that isconnected to each of the transistors Q123, Q124, Q124N, and Q123N, so asto enable generation of a plurality of output voltages for the inputanalog signal V_(IN).

For example, output voltages V111 and V112 given by equations (12) and(13): ##EQU9## appear at a connection node 111 between the resistorsR121 and R122 and a connection node 112 between the resistor R122 andthe transistor Q123, respectively.

Similarly, output voltages V113 and V114 given by equations (14) and(15): ##EQU10## appear at a connection node 113 between the resistorsR123 and R124 and a connection node 114 between the resistor 124 and thetransistor Q124, respectively.

As is understood from equations (13) and (14), the output voltages V112and B113 are equal to each other. Therefore, considering thecharacteristic that the output voltages vary more or less linearly inthe vicinity of the reference voltage V_(REF1) as the comparisonpotential, it is also understood that the output voltage V112 (or V113)internally divides the two output voltages V111 and V114 at a ratio of1:2.

On the other hand, output voltages V115 and V116, which varysymmetrically with the output voltages V111 and V112 with respect to thereference voltage V_(REF1), appear at a connection node 115 between theresistors R126 and R125, and at a connection node 116 between theresistor R126 and the transistor Q124N, respectively. The collectorcurrent I101N that is in reversed-phase with the input analog signalV_(IN) flows through the connection nodes 115 and 116.

Similarly, output voltages V117 and B118, which vary symmetrically withthe output voltages B113 and V114 with respect to the reference voltageV_(REF1), appear at a connection midpoint P117 between the resistorsR127 and R128, and at a connection midpoint 118 between the resistorR128 and the transistor Q123N, respectively.

Also in this case, the output voltages V117 and V116 are equal to eachother and the output voltage V117 (or V116) internally divides the twooutput voltages V115 and V118 at a ratio of 1:2.

FIG. 23 shows the relationship between the output voltages V113, V114,V117, V118, V111, V112, V115, and V116 and the input analog signalV_(IN).

Since the other differential amplifier 132 has the same configuration asthe differential amplifier 129, output voltages V121, V122, V125, andV126, and output voltages V119, V120, V123, and V124, which correspondto the output voltages V113 to V118 and V111 to V116 of the differentialamplifier 129, vary symmetrically with each other with respect to thereference voltage V_(REF2) (=V_(REF1) +ΔV) (see FIG. 25).

Incidentally, among the output voltages of the differential amplifiers129 and 132 of this embodiment, the output voltages V112 and V122 areequal to each other (see FIG. 24).

The comparator 110 is so constructed as to produce comparison outputswith respect to imaginary voltages V1 to V5 that equally divide theinterval between the two reference voltages V_(REF1) and V_(REF2) intosix using the relationship in which the output voltages V113 to V120internally divide the other output voltages at respective predeterminedratios.

In the above configuration, the comparison outputs of the input signalV_(IN) with respect to the reference voltages V_(REF1) and V_(REF2) andthe imaginary voltages V1 to V5 can be obtained through comparisonbetween the output voltages as shown in FIG. 26.

Here, a description is made of the following combinations.

For example, the comparison output with respect to the reference voltageV_(REF1) is obtained by comparing the output voltages V114 and V118, andthe comparison output with respect to the imaginary voltage V1 isobtained by comparing the output voltages V114 and V125.

Furthermore, the comparison outputs with respect to the virtual voltagesV2 to V5 and the reference voltage V_(REF2) can, in turn, be obtained bycomparing, for instance, the output voltages V113 and V118, V113 andV125, V111 and V125, V113 and V126, and V122 and V126, respectively (seeFIG. 27).

First, the comparison output with respect to the virtual voltage V3,which halves the reference voltages V_(REF1) and V_(REF2), is obtainedby paying attention to a pair of output voltages V114 and V118 as thecomparison outputs with respect to the reference voltage V_(REF1), andanother pair of output voltages V122 and V126 as comparison outputs withrespect to the reference voltage V_(REF2), among which the outputvoltages V114 and V126 and the output voltages V118 and V122 cross eachother at the center of the two reference voltages.

Then, the comparison output with respect to the virtual voltage V1 isobtained by using the fact that the output voltage V125 (or V124) thatcrosses the output voltage V114 internally divides the two outputvoltages V123 and V126 at a ratio of 1:2.

That is, this embodiment uses the fact that the relationship inmagnitude between the output voltages V114 and V125 (or V124) isreversed at the voltage that internally divides the reference voltageV_(REF1) and the virtual voltage V3 at a ratio of 1:2 (that is,internally divides the reference voltages V_(REF1) and V_(REF2) at aratio of 1:6).

Just as in the case of obtaining the comparison output with respect tothe imaginary voltage V1, the comparison output with respect to thevirtual voltage V5 can be obtained by using the relationship in whichthe output voltage V113 (or V112) internally divides the output voltagesV114 and V111 at a ratio of 2:1.

Furthermore, the comparison output with respect to the virtual voltageV2 can be obtained by using the output voltage V113, the relationship ofwhich in magnitude with the output voltages V125 and V126 is reversed atthe virtual voltages V3 and V5, respectively. This is based on that factthat the output voltage V125 (or V124) internally divides the outputvoltages V123 and V126 at a ratio of 1:2, and that the voltagedifference between the voltage at which the output voltages V113 andV123 cross each other and the virtual voltage V3 is a half the voltagedifference between the virtual voltages V3 and V5.

Similarly, the comparison output with respect to the virtual voltage V4is obtained by using the output voltage V117, the relationship of whichin magnitude with the output voltages V121 and V122 is reversed at thevirtual voltage V1 and V3, respectively. This is based on therelationship in which the output voltage V113 internally divides theoutput voltages V114 and V122 at a ratio of 2:1.

According to the above configuration, the comparator 110 can producecomparison outputs with respect to the virtual voltages V1 to V5 thatdivide equally into six the interval between the two reference voltagesV_(REF1) and V_(REF2) given to the respective differential amplifiers129 and 132.

Furthermore, since the resistances of the resistors constituting eachload resistor are set at the same value, the difference of the outputspeed as is caused by the difference of the time constant can be muchreduced from that of the conventional comparator.

Next, the seventeenth embodiment of this invention will be explainedusing FIG. 28.

Numeral 140 denotes a complete 8-division interpolation type comparator.In this embodiment, the comparator 140 is constructed in such a mannerthat a load resistor for a transistor Q134 (Q133N, . . . ) having arelatively large emitter area is a series connection of three resistorsR152, R153, and R154 (R157, R158 and R159, . . . ).

Furthermore, in the comparator 140, the resistances of the threeresistors R152, R153, and R154 (R157, R158, and R159, . . . ) that arein series with the transistor Q134 (Q133N, . . . ) are set at valuestwofold, onefold and onefold the resistance r of the resistors R150 andR151 (R155, R156, . . . ) connected to the counterpart transistor Q133(Q134N, . . . ), respectively.

With the above construction, an output voltage V152 given by equation(16): ##EQU11## appears at a connection node 152 between the resistorsR152 and R153. An output voltage V153 given by equation (17): ##EQU12##also appears at a connection node 153 between the resistors R153 andR154.

Similarly, an output voltage V154 given by equation (18): ##EQU13##appears at a connection node 154 between the resistor R154 and thetransistor Q133. In this embodiment, the differences between the outputvoltages V150 and V151, output voltages V151 and V152, output voltagesV152 and V153, and output voltages V153 and V154 have a ratio of1:2:2:2.

Therefore, the five pairs of in-phase output voltages V150, V151, V152,V153, and V154 and reversed-phase output voltages V155, V156, V157,V158, and V159 with respect to the reference voltage V_(REF1) have aninput-output characteristic with the input analog signal V_(IN) as shownin FIG. 29. Furthermore, the five pairs of in-phase output voltagesV160, V161, V162, V163, and V164 and reversed-phase output voltagesV165, V166, V167, V168, and V169 with respect to the reference voltageV_(REF2) have an input-output characteristic with the input analogsignal V_(IN) as shown in FIG. 30.

With the above construction, the output voltages with respect to thereference voltage V_(REF1) and the output voltages with respect to thereference voltage V_(REF2) have a relationship as shown in FIG. 31.

This embodiment uses the fact that the output voltages V154 and V159that are lowest among the in-phase and reversed-phase output voltages ofthe differential amplifier 141 cross each other at the reference voltageV_(REF1), and that the in-phase and reversed-phase output voltages V164and V169 of the differential amplifier 144 cross each other at thereference voltage V_(REF2).

This embodiment further uses the fact that the five pairs of in-phaseand reversed-phase output voltages of the differential amplifier 31 havea ratio of 1:2:2:2 with respect to imaginary voltages V1 to V7 thatequally divide the interval between the reference voltages V_(REF1) andV_(REF2) into eight, and that the five pairs of in-phase andreversed-phase output voltages of the differential amplifier 144 withrespect to the imaginary voltages V1 to V7 also have a ratio of 1:2:2:2.

For example, the comparison output with respect to the virtual voltageV1 can be obtained by comparing the output voltages V155 and V158, andthe comparison output with respect to the virtual voltage V2 can beobtained by comparing the output voltages V161 and V158.

The comparison outputs for the other virtual voltages V3 to V7 may beobtained by comparing ones selected from the combinations of the outputvoltages that cross each other at the virtual voltage concerned.

According to the above construction, the comparison outputs with respectto the virtual voltages V1 to V7 that equally divide the intervalbetween the two reference voltages V_(REF1) and V_(REF2) into eight canbe obtained by dividing the collector currents at a ratio of 1:2 as thedifferential output currents with the respective reference voltages, andby setting at 2:1:1 the resistances of the series resistors constitutingthe load resistor through which the larger collector current flows.

Since the time constants of the respective output voltages can beselected so as to be of substantially the same value, the output speedscan be made substantially equal to each other.

Next, the eighteenth embodiment of this invention will be described.

In the seventeenth embodiment described above, the load resistorconnected to the collector of the current division transistor is aseries connection of two or three resistors. However, this invention isnot limited to this case, but it may be a series connection of four ormore resistors.

Further, the nineteenth embodiment of this invention will be described.

In the seventeenth embodiment described above, the resistances of theseries resistors are set at a ratio of 1:1 or 1:2. However, the presentinvention is not limited to this case but they may be set at a ratio of1:m (m=3, 4, 5, . . . ) or other various ratios.

Further, the twentieth embodiment of this invention will be described.

In the seventeenth embodiment described above, the area ratio of thedivision transistors is set at 1:2. However, this invention is notlimited to this case, but it may be set at 1:m (m=3, 4, 5, . . . ).

In the latter case, the number and the resistance ratio of the resistorsconnected to the division transistor may be set at an arbitrary valueand ratio.

Further, the twenty-first embodiment of this invention will bedescribed.

In the above embodiments, the collector current as the comparison outputof the input analog signal V_(IN) with respect to each of the referencevoltages V_(REF1) and V_(REF2) is divided into two currents. However,this invention is not limited to this case, but it may be divided intothree or more currents.

In the latter case, the number and the resistance ratio of the resistorsconnected to the division transistor may be set at an arbitrary valueand ratio.

Furthermore, the twenty-second embodiment of this invention will bedescribed.

The above embodiments are concerned with a comparator of the type whichproduces comparison outputs of an input analog signal with respect to aplurality of virtual voltages simply by supplying it with two referencevoltages V_(REF1) and V_(REF2). However, this invention is not limitedto this case, but a comparator having this function may be used as acomparator in an A-D converter or other electronic circuits.

As described above, according to this invention, each of the comparisonoutput currents with respect to each reference potential is divided at apredetermined ratio thus generating a plurality of divided outputcurrents, and the output voltage generated by each divided comparisonoutput current is further divided by an output means into a plurality ofoutput voltages. Thereafter, the combination of output voltages, therelationship of which in magnitude is reversed at an intermediatepotential between the first and second reference voltages, is selectedand a comparison is made between those output voltages. Thus, a voltagecomparison amplifier can easily be obtained which can produce comparisonoutputs for an input analog signal with respect to arbitrary imaginaryvoltages between the two reference potentials actually Given.

Next, the twenty-third embodiment of this invention will be explained.

The construction and the operation of the series-parallel converter inwhich the interpolation method and the Vernier method are adopted forthe comparator which is the principle described above.

In FIG. 32, 190 shows a serial-parallel A-D converter circuit as awhole. It is made so that the input terminal and the lowest levelpotential V_(REFB) are connected with an array of voltage dividingresistors R (R_(F1), R_(F2), . . . , R_(F16)) and current source I191and an input analog signal V_(IN) is fetched from the connectionterminal of each resistance constituting an array of voltage dividingresistors array by dividing at a predetermined ratio.

First, an A-D converter circuit 190 supplies input signal V_(IN),reference potential V_(REFT), and V_(REFB) to a high-order comparator198, obtains a comparison output for two reference potentials V_(REFT)and V_(REFB) by use of two-division interpolation using complementaryoutput explained above and a comparison output for an intermediatepotential V2 (reference voltage V_(U2) in a conventional example) whichdivides the above comparison output into two parts, and outputs these atthe output composite circuit 195 and switch circuit 196.

A switch circuit 196 obtains from these three sets of comparison outputswhich range the potential of input signal V_(IN) belongs to among thefour voltage ranges in which two reference potentials V_(REFT) andV_(REFB) are divided into equal parts and outputs bias currents I191,I192, I193, and I194 to the current source of low-order comparators CDito CDi+2 (i=1, 4, 7, or 10) for three sets of low-order comparatorswhich are lined in the same array among 12 sets of low-order comparatorsarranged in four arrays.

By the above, the A-D converter circuit shifts to the comparisonoperation between the corresponding attenuated analog signals VIi toVIi+2 (i=1, 4, 7, or 10) and the reference voltages V_(REFi) toV_(REFi+2) (i=1, 4, 7, or 10) with respect to the selected three sets oflow-order comparators CDi to CD(i+2) (i=1, 4, 7 or 10).

The reference voltages V_(REFi) is a voltage given from the connectionterminal of each reference resistance r_(Fi) of a reference resistancearray r (r_(F1), r_(F2), . . . , r_(F16)) which are connected betweentwo reference voltages V_(REFT) and V_(REFB). The current value of thecurrent source I192 which is connected between the array of thereference resistors r and the reference voltage V_(REFB) is set a thesame value as the current source I191. The resistance value of eachreference resistance r_(Fi) is set at a value two times the resistancevalue of each divider resistance R_(Fi).

Therefore, the attenuated analog signals Vi to Vi+2 (i=1, 4, 7, or 10)which is inputted to low-order comparators CDi to CDi+2 (i=1, 4, 7, or10) is attenuated with a one half voltage gradient for the voltagegradient of the reference voltage as explained in the first section.That is, the input analog signal V_(IN) is equivalently expanded twotimes and inputted.

The A-D converter circuit 190 converts this comparison output intobinary data by use of a low-order encoder 197, synthesizes this resultof comparison and the previously obtained high-order result ofcomparison at an output composite circuit 195, and outputs as digitaldata.

According to the construction mentioned above, the A-D converter circuit190 can attenuate the input signal V_(IN) through the array of thevoltage dividing resistors R, compare the equivalently expanded inputsignal V_(IN) with the reference voltage by comparing the attenuatedsignal V_(INi) with each reference voltage, and improve the SN ratiocompared to conventional ones.

In addition, since the high-order comparators are interpolated bytwo-division, the number of high-order comparators can be reduced. As aresult, the arrangement of high-order comparators can be made simple.

Therefore, power consumption of an A-D converter circuit built-insemiconductor integrated circuit can be reduced compared to conventionalones and chip area can also be made small.

In addition, materialization of a 10-bit or higher A-D converter circuitbecomes easier. It is suitable for the signal processing circuit forhigh resolution digital display which is used in high definitiontelevision sets.

Next, the twenty-fourth embodiment of this invention will be described.

Furthermore, a case where the voltage gradient of input signal V_(IN)which is attenuated by a voltage dividing resistor is set at one halfthe voltage gradient of the reference voltage which is given to eachcomparator has been described in the twenty-third embodiment. However,this invention is not limited to this, but may be widely applied even incases where the voltage gradient by use of voltage dividing resistors isset at a value greater than one half the voltage gradient of a referencevoltage and at a value smaller than that.

In addition, the twenty-fifth embodiment of this invention will bedescribed. A case where the resistance ratio of voltage dividingresistors and reference resistors is made 1 to 2 and a constant-currentsource I191 which leads in the same constant current I is connected toeach array of voltage dividing resistors has been described in thetwenty-third embodiment. However, this invention is not limited to this,but the values of the divider resistance and the reference resistancemay be made the same and the ratio of the constant current flowing inthe constant-current source which is connected with each voltagedividing resistors array can be set at 1 to 2.

Furthermore, the twenty-sixth embodiment of this invention will bedescribed.

A case where the comparison output of high-order comparator isinterpolated by two-division has been described in the twenty-thirdembodiment. However, this invention is not limited to this, but may bewidely applied even in cases the reference potentials V_(REFT) andV_(REFB) are interpolated by four-division and, further, in cases ofsix-division and seven-division by use of principle similar to that.

The twenty-seventh embodiment of this invention will be described.

A case where two sets of high-order comparators are used and five setsof reference voltages are generated from two reference potential (thatis, four-division interpolation is carried out) has been described inthe twenty-third embodiment. However, this invention is not limited tothis, but it can be made so that, of collector currents in which acomparison output of a predetermined reference voltage is divided, thein-phase output is outputted to low-order comparators and the reversedphase output is inputted from high-order comparators and synthesized. Inaddition, the opposite combination is also applicable.

As mentioned above, according to this invention, a comparison output fora virtual reference voltage level V2 which divides a first referencevoltage level which is actually generated into two parts is obtained bymeans of interpolation by comparing analog signal with the firstreference voltage level in the high-order comparator section and, of itscomparison output, by comparing the in-phase output signal andreversed-phase output signal obtained for reference voltage levels whichare different from each other, and a second reference voltage levelwhich is inputted to the low-order comparator section is switched. Andafter that, the comparison of analog signal, which is divided by meansof a plurality of resistors which are connected in series, with thefirst reference voltage level allows the reduction of the number oftransistors considerably compared to conventional ones, which are neededto constitute the high-order comparator section, and a serial-parallelanalog-to-digital converter circuit with a small circuit area for itsresolution capability can be obtained easily.

Next, the twenty-eighth embodiment of this invention will be explained.

The conversion process by use of serial-parallel analog-to-digitalconverter circuit will be described.

A serial-parallel A-D converter circuit in which the above principle isused in the low-order comparators is shown in FIG. 33. In FIG. 33, 210shows a serial-parallel A-D converter circuit as a whole. It is made sothat the input terminal and the lowest level potential V_(REFB) areconnected with an array of voltage dividing resistors R (R_(G1), R_(G2),. . . , R_(G16)) and current source I116 and an input analog signalV_(IN) is fetched from the connection terminal of each resistorconstituting dividing resistor by dividing at a predetermined ratio.

First, an A-D converter circuit 210 compares the attenuated analogsignals V_(IN4), V_(IN8), and V_(IN12), which are generated by means ofvoltage dividing resistors R, with reference voltages VU1, VU2, and VU3,which are obtained by means of the array of reference resistors r, incomparators 2AG, 2BG, and 2CG, and outputs comparison output at anoutput composite circuit 211 through an AND circuit 213 as well as atthe current source of low-order comparators as a bias voltage.

By the above, of the 12 sets of low-order comparators arranged in fourrows, three sets of low-order comparators in the same row are selected.The A-D converter circuit 210 compares attenuated analog signals VIi toVIi+2 (i=1, 4, 7, or 10) with reference voltages V_(REFi) to V_(REFi+2)(i=1, 4, 7, or 10) corresponding to them in these three sets oflow-order comparators CEi to CE(i+2) (i=1, 4, 7, or 10).

The reference voltages V_(REFi) is given from the connection terminal ofeach reference resistor r_(Gi) of an array of reference resistors r(r_(G1), r_(G2), . . . , r_(G16)) which are connected between tworeference voltages V_(REFT) and V_(REFB). In addition, the current valueof the current source I117 which is connected between the array ofreference resistors r and the reference voltage V_(REFB) is the samevalue as the current source I116. The resistance value of each referenceresistor r_(Gi) is set at a value two times the resistance value of eachdividing resistor R_(Gi).

Therefore, the attenuated analog signals Vi to Vi+2 (i=1, 4, 7, or 10)which is supplied to low-order comparators CEi to CE(i+2) (i=1, 4, 7, or10) is attenuated with a one half voltage gradient corresponding to thevoltage gradient of the reference voltage as explained in the firstsection. This means that the input analog signal V_(IN) is equivalentlyexpanded two times.

The A-D converter circuit 210 obtains a comparison output of theattenuated analog signal for a virtual potential V2 which divides eachreference voltage into two parts or a virtual potential which divideseach reference voltage into four parts by using either of the twointerpolation principles explained above.

For example, in cases where a comparison output for a virtual potentialwhich divides a virtual voltage into two parts is obtained, when acomparison output for each reference voltage Vi is supplied fromlow-order comparators CEi (i=1, 2, . . . , 12), a low-order encoder 223obtains a comparison output including a virtual potential which furtherdivides two reference potentials by comparison outputs which are inreversed-phase relationship with each other among comparative outputs tobe outputted with respect to two reference potentials.

Then, this result of comparison is outputted to an output compositecircuit 211 and combined with the result of high-order comparison whichwas inputted first, thereby outputting digital data in which inputanalog signal V_(IN) is converted by high resolution for a referencepotential generated by an array of reference resistors r.

According to the configuration mentioned above, the A-D convertercircuit 210 can attenuate the input signal V_(IN) through the voltagedividing resistors R, compare the equivalently expanded input signalV_(IN) with the reference voltage by comparing the attenuated signalV_(INi) with each reference voltage, and improve the S/N ratio comparedto conventional ones.

In addition, a high resolution for the resolution which is actuallygenerated by an array of reference resistors r can be materialized bytwo-division or four-division interpolating the comparison output of thelow-order comparator, and the number of elements can be reducedconsiderably.

As a result, power consumption of an A-D converter circuit built-insemiconductor integrated circuit can be reduced compared to conventionalones and the chip area can also be made small.

In addition, materialization of a 10-bit or higher A-D converter circuitbecomes easier. It is suitable for the signal processing circuit forhigh resolution digital display which is used in high definitiontelevision sets.

Next, the twenty-eighth embodiment of this invention will be described.

Furthermore, a case where the voltage gradient of input signal V_(IN)which is attenuated by a dividing resistor is set at one half thevoltage gradient of the reference voltage which is given to eachcomparator has been described in the twenty-seventh embodiment. However,this invention is not limited to this, but can be widely applied even incases where the voltage gradient by use of voltage dividing resistors isset at a value greater than one half the voltage gradient of a referencevoltage and at a value smaller than that.

In addition, the twenty-ninth embodiment will be described in thetwenty-seventh embodiment, a case where the resistance ratio of voltagedividing resistors and reference resistors are made 1 to 2 and aconstant-current source I116 which leads in the same constant current Iis connected to each resistor array has been described. However, thisinvention is not limited to this, but the values of the dividingresistors and the reference resistors may be made the same and the ratioof the constant current flowing in the constant-current source which isconnected with each resistance array can be set at 1 to 2.

Next, the thirtieth embodiment of this invention will be described.

Furthermore, a case where the comparison output of each comparator CDiis interpolated by four-division has been described in thetwenty-seventh embodiment. However, this invention is not limited tothis, but may also be designed to output the in-phase outputs of thedivided collector current to the low-order comparator and to combine thereversed-phase outputs by inputting them from the high-order comparator.The combination opposite to this may also be applied.

Next, the thirty-first embodiment of this invention will be described.

Furthermore, a case where the comparison output of the comparator isinterpolated and the comparison output for the virtual potentialsbisectional or quadrisectional between reference voltages is obtainedhas been described in the twenty-seventh embodiment. However, thisinvention is not limited to this, but may also be widely applied incases where a comparison output which divides the reference voltage intosix equal parts, eight equal parts, and so on, is obtained.

As mentioned above, according to this invention, an analog signal isdivided by means of a plurality of resistances connected in series, andthe analog signals are inputted to the low-order comparator section andcompared with the first reference voltage level. Then, of a pair ofin-phase output signal and reversed-phase signal which are thecomparison outputs of it, the in-phase output signal and reversed-phaseoutput signal are compared, which are obtained for the reference voltagelevels which are different from each other, thereby obtaining byinterpolation a comparison output for a virtual reference voltage levelwhich divides the actually generated first reference voltage level intotwo parts, and a serial-parallel analog-to-digital converter circuitwith a small circuit area for its resolution capability can be obtainedeasily.

While there has been described in connection with the preferredembodiments of the invention, it will be obvious to those skilled in theart that various changes and modifications may be aimed, therefore, tocover in the appended claims all such changes and modifications as fallwithin the true spirit and scope of the invention.

What is claimed is:
 1. An analog-digital convertor circuit for enteringto comparing means a plurality of reference voltages each divided by aselected voltage gradient and an input analog signal and outputting saidinput analog signal by converting said signal into a digital signal,wherein:said input analog signal is inputted to an array of resistors inwhich a plurality of resistors are connected in series; said inputanalog signal is attenuated by a nonlinear voltage gradient via saidarray of resistors and is inputted to said plurality of comparison meansas an attenuated analog signal; and said input analog signal isconverted into the digital signal based on the result of comparisonbetween said attenuated analog signal and said plurality of referencevoltages.
 2. An analog-digital convertor circuit according to claim 1,wherein:each resistor in said array of resistors has a plurality ofresistors connected in series which establish a non-linear relationshipamong respective resistance values of the resistors; and said array ofresistors successively attenuates said input analog signal with eachresistor, and outputs attenuated analog signals from points ofconnection between each resistor.
 3. An analog-digital convertor circuitaccording to claim 1, wherein said plurality of resistors connected inseries establishes a geometrical progression among respective resistancevalues of the resistors.
 4. An analog-digital convertor circuitaccording to claim 3, wherein the resistance value of said array ofresistors is one half the resistance value of a second array ofresistors, said second array of resistors providing a predeterminedvoltage gradient to said reference voltage.
 5. An analog-digitalconvertor circuit according to claim 4, wherein the resistance of eachresistor in said array of resistors is small compared with theresistance of a corresponding resistor in said second array ofresistors.
 6. An analog-to-digital converter comprising:a referenceresistor array consisting of a plurality of resistor means connected inseries arrangement and dividing the reference voltage across saidplurality of resistor means connected in series arrangement into aplurality of reference potentials; an array of voltage dividing resistormeans consisting of a plurality of resistor means connected in seriesarrangement and dividing the potential difference between an analoginput signal supplied to one end of said series arrangement of saidplurality of resistor means and a predetermined potential supplied toanother end of said series arrangement of said plurality of resistormeans into a plurality of divided analog signals attenuated by a voltagegradient which is different from the voltage gradient provided by saidplurality of reference potentials; a plurality of differentialamplification means for comparing said plurality of divided analogsignals with said plurality of reference potentials corresponding tosaid divided analog signals, respectively, and outputting in-phaseoutput signals and reversed-phase output signals; a plurality of firstcomparison means for comparing in-phase output signals withreversed-phase output signals corresponding to the mutually equivalentreference potentials with respect to said plurality of referencepotentials and outputting the comparison output of said divided analogsignals corresponding to the respective reference potentials; aplurality of second comparison means for comparing in-phase outputsignals with reversed-phase output signals corresponding to mutuallydiffering potentials with respect to mutually adjacent potentials ofsaid plurality of reference potentials and outputting the comparisonoutput of said divided analog signals with regard to virtual referencepotentials bisecting the space between the reference potentials; and anencoding means for converting said analog input signals into digitaldata of predetermined resolution on the basis of comparison output inputfrom said first and said second comparison means; wherein the voltagegradient of said array of voltage dividing resistor means is half thevoltage gradient of said plurality of reference potentials.
 7. Aserial-parallel type analog-to-digital converter, which converts analoginput signals into digital data a plurality of times by a predeterminednumber of bits at a time, comprising:a reference resistor arrayconsisting of a plurality of resistor means connected in series anddividing the reference voltage across said plurality of resistor meansconnected in series to a plurality of reference potentials; a voltagedividing resistor array consisting of a plurality of resistor meansconnected in series and dividing the potential difference between ananalog input signal applied to one end of said plurality of resistormeans connected in series and a predetermined potential supplied to theother end of said plurality of resistor means to a plurality of dividedanalog signals attenuated by a voltage gradient which is different froma voltage gradient of said plurality of reference potentials; aplurality of differential amplification means for comparing saidplurality of divided analog signals with said plurality of referencepotentials corresponding to said divided analog signals, respectively,and outputting in-phase output signals and reversed-phase outputsignals; a plurality of first comparison means for comparing in-phaseoutput signals with reversed-phase output signals corresponding to themutually equivalent reference potentials with respect to said pluralityof reference-potentials and outputting the comparison output of saiddivided analog signals corresponding to the respective referencepotentials; a plurality of second comparison means for comparingin-phase output signals with reversed-phase output signals correspondingto mutually differing potentials with respect to mutually adjacentpotentials of said plurality of reference potentials and outputting thecomparison output of said divided analog signals corresponding to thevirtual reference potentials bisecting the space between the referencepotentials; and an encoding means for converting said analog inputsignals into digital data of a predetermined resolution on the basis ofcomparison output input from said first and said second comparisonmeans; wherein the voltage gradient of said plurality of divided analogsignals is set at half the voltage gradient of said plurality ofreference potentials.
 8. An analog-to-digital converter comprising:areference resistor array consisting of a plurality of resistor meansconnected in series and dividing the reference voltage across saidplurality of resistor means connected in series into a plurality ofreference potentials; an array of voltage dividing resistors consistingof a plurality of resistor means-connected in series and dividing thepotential difference between an analog input signal supplied to one endof said plurality of resistor means connected in series, and apredetermined potential applied to another end by said plurality ofresistor means into a plurality of divided analog signals attenuated bya voltage gradient which is different from voltage gradient of saidplurality of reference potentials; a plurality of differentialamplification means for comparing said plurality of analog signals withsaid plurality of reference potentials corresponding to said analogsignals, respectively, and outputting in-phase output currents andreversed-phase output currents; a current dividing means for dividingin-phase output currents and reversed-phase output currentscorresponding to said plurality of reference potentials as dividedin-phase output currents and divided reversed-phase output currents,respectively; a current composition means for generating a compositein-phase output current by adding a plurality of divided in-phase outputcurrents generated corresponding to mutually adjacent referencepotentials at a predetermined proportion or generating a compositereversed-phase output current by adding a plurality of dividedreversed-phase output currents generated corresponding to mutuallydiffering reference potentials in a predetermined proportion; aplurality of first comparison means for comparing divided in-phaseoutput currents with divided reversed-phase output currentscorresponding to mutually equivalent reference potentials with respectto said plurality of reference potentials and outputting the comparisonoutput of said divided analog signals corresponding to the respectivereference potentials; a plurality of second comparison means forcomparing divided in-phase output signals with divided reversed-phaseoutput signals corresponding to mutually differing potentials withrespect to mutually adjacent potentials of said plurality of referencepotentials and outputting the comparison output of said divided analogsignals corresponding to virtual reference potentials bisecting thespace between the reference potentials; a plurality of third comparisonmeans for comparing said plurality of composite in-phase output currentswith said divided reversed-phase output current, respectively, or elsesaid plurality of composite reversed-phase output currents with saidplurality of divided in-phase output currents, and outputting thecomparison output of said divided analog signals corresponding tovirtual reference potentials multiply uniform between the referencepotentials; and an encoding means for converting said analog inputsignals into digital data of predetermined resolution on the basis ofcomparison output input by said first, said second, or said thirdcomparison means.
 9. An analog-to-digital converter according to claim8, wherein the voltage gradient of said plurality of analog signals ishalf the voltage gradient of said plurality of reference potentials. 10.An analog-to-digital converter according to claim 8, wherein:saidcurrent dividing means divides said in-phase output currents as firstand second divided in-phase output currents at a current ratio of 1:2,respectively, and divides said reversed-phase output currents as firstand second divided reversed-phase output currents at a current ratio of1:2, respectively; said current composition means generates a compositein-phase output current by adding the first divided in-phase outputcurrents corresponding to mutually adjacent reference potentials andgenerates a composite reversed-phase output current by adding the firstdivided reversed-phase output currents corresponding to referencepotentials neighboring to each other; said first comparison meanscompares said second divided in-phase output currents with said seconddivided reversed-phase output currents corresponding to mutuallyequivalent reference potentials with respect to said plurality ofreference potentials, and outputs the comparison output of said dividedanalog signals corresponding to their respective reference potentials;said second comparison means compares said second divided in-phaseoutput signals with said second divided reversed-phase output signalscorresponding to mutually differing potentials with respect to themutually adjacent potentials of said plurality of reference potentials,and outputs the comparison output of said divided analog signalscorresponding to virtual reference potentials bisecting the spacebetween reference potentials; and said third comparison means comparessaid composite in-phase output currents with said second dividedreversed-phase output currents, respectively, in pairs corresponding toadjacent reference potentials or else said composite reversed-phaseoutput currents with said second divided in-phase output currents,respectively, in pairs, and outputs the comparison output of saiddivided analog signals corresponding to virtual reference potentialsquadrisecting the space between the reference potentials.
 11. Aserial-parallel type analog-to-digital converter, which converts analoginput signals into digital data a plurality of times by a predeterminednumber of bits at a time, comprising:a reference resistor arrayconsisting of a plurality of resistor means connected in series anddividing the reference voltage across said plurality of resistor meansconnected in series into a plurality of reference potentials; a voltagedividing resistor array consisting of a plurality of resistor meansconnected in series and dividing the potential difference between ananalog input signal supplied to one end of said plurality of resistormeans connected in series and a predetermined potential supplied toanother end of said plurality of resistor means into a plurality ofdivided analog signals attenuated by a voltage gradient which isdifferent from a voltage gradient of said plurality of referencepotentials; a plurality of differential amplification means forcomparing said plurality of divided analog signals with said pluralityof reference potentials corresponding to said divided analog signals,respectively, and outputting in-phase output currents and reversed-phaseoutput currents; a current dividing means for dividing in-phase outputcurrents and reversed-phase output currents corresponding to saidplurality of reference potentials as divided in-phase output currentsand divided reversed-phase output currents, respectively; a currentcomposition means for generating a composite in-phase output current byadding a plurality of divided in-phase output currents generatedcorresponding to mutually adjacent reference potentials in apredetermined proportion or generating a composite reversed-phase outputcurrent by adding a plurality of divided reversed-phase output currentsgenerated corresponding to mutually differing reference potentials in apredetermined proportion; a plurality of first comparison means forcomparing divided in-phase output currents with divided reversed-phaseoutput currents corresponding to mutually equivalent referencepotentials with respect to said plurality of reference potentials andoutputting the comparison output of said divided analog signalscorresponding to the respective reference potentials; a plurality ofsecond comparison means for comparing divided in-phase output signalswith divided reversed-phase output signals corresponding to mutuallydiffering potentials with respect to mutually adjacent potentials ofsaid plurality of reference potentials and outputting the comparativeoutput of said divided analog signals corresponding to virtual referencepotentials bisecting the space between reference potentials; a pluralityof third comparison means for comparing said plurality of compositein-phase output currents with said divided reversed-phase outputcurrent, respectively, or else said plurality of composite reverse phaseoutput currents with said plurality of divided in-phase output currents,respectively, and outputting the comparative output of said dividedanalog signals corresponding to virtual reference potentials multiplyuniform between the reference potentials; and an encoding means forconverting said analog input signals into digital data of apredetermined resolution on the basis of comparison output input by saidfirst, said second, or said third comparison means.
 12. Aserial-parallel type analog-to-digital converter according to claim 11,wherein the voltage gradient of said plurality of divided analog signalsis half the voltage gradient of said plurality of reference potentials.13. A serial-parallel analog-to-digital converter according to claim 11,wherein:said current dividing means divides said in-phase outputcurrents as first and second divided in-phase output currents,respectively, at a current ratio of 1:2 and divides said reversed-phaseoutput currents as first and second divided reversed-phase outputcurrents, respectively, at a current ratio of 1:2; said currentcomposition means generates a composite in-phase output current byadding the first divided in-phase output currents corresponding tomutually adjacent reference potentials, and generates a compositereversed-phase output current by adding the first divided reversed-phaseoutput currents corresponding to mutually adjacent reference potentials;said first comparison means compares said second divided in-phase outputcurrents with said second divided reversed-phase output currentscorresponding to mutually equivalent reference potentials with respectto said plurality of reference potentials, and outputs the comparisonoutput of said divided analog signals corresponding to their respectivereference potentials; said second comparison means compares said seconddivided in-phase output signals with said second divided reversed-phaseoutput signals corresponding to mutually differing potentials withrespect to the mutually adjacent potentials of said plurality ofreference potentials, and outputs the comparison output of said dividedanalog signals corresponding to virtual reference potentials bisectingthe space between reference potentials; and said third comparison meanscompares said composite in-phase output currents with said seconddivided reversed-phase output currents, respectively, in pairscorresponding to neighboring reference potentials, or else compares saidcomposite reversed-phase output currents with said second dividedin-phase output currents, respectively, in pairs, and outputs thecomparative output of said divided analog signals corresponding tovirtual reference potentials quadrisecting the space between referencepotentials.
 14. A serial-parallel analog-to-digital converter circuitwhich converts an analog signal into digital data by dividing saidanalog signal into two steps of high-order bits and low-order bits,comprising:a high-order comparator section which obtains high-order bitsby comparing said analog signal with a plurality of first referencevoltage levels, wherein said high-order comparator provides in-phaseoutput signals and reversed-phase output signals by comparing the firstreference voltage levels with said analog signal with respect to each ofsaid first reference voltage levels, and obtains a comparative outputfor a virtual reference voltage level which divides said first referencevoltage levels into two parts by comparing in-phase output signals withreversed-phase output signals, and converts said analog signal intohigh-order bits by use of a comparative output for said virtualreference voltage level in addition to said first reference voltagelevels; and a low-order comparator section which obtains low-order bitsby comparing a plurality of second reference voltage levels obtainedfrom said high-order comparator section with said analog signal, whereinsaid analog signal is converted into low-order bits by dividing saidanalog signal with a voltage gradient by means of a plurality ofresistances which are connected in series.
 15. A series-parallelanalog-to-digital converter circuit according to claim 14, wherein thevoltage gradient of said analog signal, which is divided with a voltagegradient different from the voltage gradient of said second referencevoltage levels by means of said resistances which are connected inseries, is set at one half the voltage gradient of said referencevoltage level.
 16. A serial-parallel analog-to-digital converter circuitwhich converts analog signal into digital data by dividing said analogsignal into two steps of high-order bits and low-order bits, wherein:ahigh-order comparator section obtains high-order bits by comparing saidanalog signal with a plurality of first reference voltage levels andobtains a pair of in-phase output signals and reversed-phase outputsignals by comparing the first reference voltage levels with said analogsignal with respect to each of said first reference voltage levels, andafter that, generates a plurality of in-phase shunt signals andreversed-phase shunt signals by dividing the in-phase output signal andreversed-phase output signal at a predetermined rate, generates anin-phase composite signal and a reversed-phase composite signal byadding in-phase shunt signals and reversed-phase shunt signals at apredetermined rate, which were generated with respect to referencevoltage levels which are different from each other among the in-phaseshunt signals and reversed-phase shunt signals, obtains a comparisonoutput for a virtual reference voltage level which divides said firstreference voltage levels at a predetermined rate by comparing saidin-phase shunt signals with said reversed-phase composite signal or saidreversed-phase shunt signals with said in-phase composite signal, andconverts said analog signal into high-order bits by use of a comparisonoutput for said virtual reference voltage levels in addition to saidfirst reference voltage levels, and wherein a low-order comparatorsection which obtains low-order bits by comparing a plurality of secondreference voltage levels, which are set based on the result ofcomparison of said high-order comparator section, with said analogsignal converts said analog signal, which is divided with a voltagegradient different from the voltage gradient of said second referencevoltage levels by means of a plurality of resistors which are connectedin series, with said second reference voltage levels.
 17. Aserial-parallel analog-to-digital converter circuit which converts ananalog signal into digital data by dividing said analog signal into twosets of high-order bits and low-order bits, wherein:a high-ordercomparator section which obtains high-order bits by comparing saidanalog signal with a plurality of first reference voltage levels,wherein said high-order comparator provides in-phase output signals andreversed-phase output signals by comparing the first reference voltagelevels with said analog signal with respect to each of said firstreference voltage levels, and after that, generates two sets of in-phaseshunt signals and two sets of reversed-phase shunt signals by dividingthe in-phase output signal and reversed-phase output signal at the ratioof 1 to 2, generates an in-phase composite signal and a reversed-phasecomposite signal by adding in-phase shunt signals and reversed-phaseshunt signals at the ratio of 1 to 1, which were generated with respectto reference voltage levels which are different from each other amongtwo sets of in-phase shunt signals and two sets of reversed-phase shuntsignals, obtains comparison outputs for three sets of virtual referencevoltage levels which divide said first reference voltage levels intofour equal parts, respectively, by comparing said two sets of in-phaseshunt signals with said reversed-phase composite signal or said two setsof reverse phase shunt signals with said in-phase composite signal, andconverts said analog signal into high-order bits by use of comparisonoutputs for said three sets of virtual reference voltage levels inaddition to said first reference voltage levels, and wherein a low-ordercomparator section which obtains low-order bits by comparing a pluralityof second reference voltage levels, which are set based on the result ofcomparison of said high-order comparator section, with said analogsignal converts said analog signal into low-order bits by comparing saidanalog signal, which is divided with a voltage gradient different fromthe voltage gradient of said second reference voltage levels by means ofa plurality of resistors which are connected in series, with said secondreference voltage levels.
 18. A serial-parallel analog-to-digitalconverter circuit which converts analog signal into digital data bydividing conversion operation into two steps of high-order bits andlow-order bits, wherein:a low-order comparator section which obtainslow-order bits by comparing a plurality of first reference voltagelevels obtained as a result of comparison of a high-order comparatorsection with said analog signal supplies said analog signal, which isdivided with a voltage gradient different from the voltage gradient ofsaid first reference voltage levels by means of a plurality of resistorswhich are connected in series, obtains a pair of in-phase output signaland reversed-phase output signal by comparing the first referencevoltage levels with said analog signal which is divided by means ofresistors with respect to each of said first reference voltage levels,obtains a comparison output responding to a virtual reference voltagelevel which divides said first reference voltage levels into two partsby comparing in-phase output signal with reversed-phase output signalobtained in correspondence with reference voltage levels which aredifferent from each other, and converts said analog signal intolow-order bits by use of a comparison output responding to said virtualreference voltage level in addition to said first reference voltagelevels.
 19. A serial-parallel analog-to-digital converter circuitaccording to claim 18, wherein the voltage gradient of said analogsignal, which is divided with a voltage gradient different from thevoltage gradient of said first reference voltage levels by means of saidresistors which are connected in series, is set at one half the voltagegradient of said first reference voltage level.
 20. A serial-parallelanalog-to-digital converter circuit which converts an analog signal intodigital data by dividing said analog signal into two steps of high-orderbits and low-order bits, whereina low-order comparator sectional whichobtains low-order bits by comparing a plurality of first referencevoltage levels that result from a comparison of a high-order comparatorsection with said analog signal, supplies said analog signal, which isdivided with a voltage gradient different from the voltage gradient ofsaid first reference voltage levels, by means of a plurality ofresistors which are connected in series, obtains a pair of in-phaseoutput signal and reversed-phase output signal by comparing the firstreference voltage levels with said analog signal, which is divided bymeans of resistors, with respect to each of said first reference voltagelevels, and after that, generates a plurality of in-phase shunt signalsand reversed-phase shunt signals by dividing the in-phase output signaland reversed-phase output signal at a predetermined rate, generates anin-phase composite signal and a reversed-phase composite signal byadding in-phase shunt signals and reversed-phase shunt signals at apredetermined rate, which were generated with respect to referencevoltage levels which are different from each other among the in-phaseshunt signals and reversed-phase shunt signals, obtains a comparisonoutput responding to a virtual reference voltage level which dividessaid first reference voltage levels at a predetermined rate by comparingsaid in-phase shunt signals with said reversed-phase composite signal orsaid reversed-phase shunt signals with said in-phase composite signal,and converts said analog signal into low-order bits by use of acomparison output responding to said virtual reference voltage levels inaddition to said first reference voltage levels.
 21. A serial-parallelanalog-to-digital converter circuit which converts an analog signal intodigital data by dividing conversion operation into two steps ofhigh-order bits and low-order bits, wherein:a low-order comparatorsection which obtains low-order bits by comparing a plurality of firstreference voltage levels that result from a comparison of a high-ordercomparator section with said analog signal, supplies said analog signal,which is divided with a voltage gradient different from the voltagegradient of said first reference voltage levels, by means of a pluralityof resistors which are connected in series, obtains a pair of in-phaseoutput signal and reversed-phase output signal by comparing the firstreference voltage levels with said analog signal, which is divided bymeans of resistors, with respect to each of said first reference voltagelevels, and after that, generates two sets of in-phase shunt signals andtwo sets of reversed-phase shunt signals by dividing the in-phase outputsignal and reversed-phase output signal at the ratio of 1 to 2,generates an in-phase composite signal and a reversed-phase compositesignal by adding in-phase shunt signals and reversed-phase shunt signalsat the ratio of 1 to 1, which were generated with respect to referencevoltage levels which are different from each other among two sets ofin-phase shunt signals and two sets of reversed-phase shunt signals,obtains a comparison output corresponding to three sets of virtualreference voltage levels which divide said first reference voltagelevels into four equal parts, respectively, by comparing said two setsof in-phase shunt signals with said reversed-phase composite signal orsaid two sets of reversed-phase shunt signals with said in-phasecomposite signal, and converts said analog signal into low-order bits byuse of a comparison output corresponding to said three sets of virtualreference voltage levels in addition to said first reference voltagelevels.